This invention relates to an image forming apparatus for forming a toner image on a rotating photoreceptor drum by an electrophotographic method to carry out image formation and to a method of controlling the rotational peripheral speed of said rotating photoreceptor drum to make it constant.
In an image forming apparatus based on an electrophotographic method, it is put into practice that a toner image is formed on a rotating image carrying member made up of a photoreceptor drum or a photoreceptor belt and the formed toner image is directly or indirectly transferred onto a sheet of recording paper and fixed. In forming an image, image exposure is carried out by an image exposure means on an image carrying member which has been uniformly charged by a charging means, to form a latent image; in forming a latent image, if the peripheral speed of the image carrying member which is rotating at a constant speed fluctuates, some distortion of the formed image is brought about. Further, in a color image forming apparatus of a tandem type, a plurality of monochromatic images formed by the respective monochromatic image forming units are superposed together to form a color image on a sheet of recording paper, it is regarded as an essential condition for obtaining a good-quality color image that the image carrying members in the respective monochromatic image forming units have the same speed and have no speed fluctuation.
As regards the speed control of a photoreceptor drum, control methods using various kinds of speed detecting means have been proposed; however, if it is intended to control the angular speed of a photoreceptor drum in real time to make it constant, a rotational speed control method for practicing the control of rotational speed using an angular speed detecting means based on an encoder is used.
In the publication of the unexamined patent application H6-327278, for the angular speed control of a photoreceptor drum, it is proposed that the profile of the rotational fluctuation of a photoreceptor drum at a certain timing is measured by the use of a feedback control method or a feed-forward control method, and the angular speed control is carried out until the next specified sampling timing by using the data. This proposal has been done by taking it into consideration to control a factor of a rotating photoreceptor drum having no reproducibility by using a feedback control process. However, in the above-mentioned proposal, the control is such that only the factor of rotational fluctuation which happens to be generated during the sampling timing is suppressed. Further, as regards the feedback control, if it is intended to suppress a wide-range rotational fluctuation, a high-priced CPU, a high-resolution encoder, etc. are required, which makes the feedback control not realistic.
On the other hand, if a peripheral speed detecting means based on an encoder is used for the detection of the peripheral speed of an image carrying member, the structure becomes mechanically complex, and the speed detecting means becomes high in price. For a tandem-type color image forming apparatus, because a plurality of speed detecting means are required, this problem becomes more remarkable.
It is also an object of this invention to provide a rotational speed control method in which a speed detecting means based on an encoder is not used, marking is made on a rotary body such as an image carrying member by a writing means, and the speed control of the rotary body is performed by carrying out a low-cost high-precision peripheral speed detection based on the detection of the marking.
Further, in an image forming apparatus employing the above-mentioned speed control method, marking toner particles of the marking adhere to the circumferential surface of the image carrying member, and a problem of toner consumption being of large amount and a problem of the surface of the image carrying member being smudged are produced.
To overcome the abovementioned drawbacks in conventional image-recording apparatus, it is the first object of the present invention to provide a drive control method of a photoreceptor drum to actualize that rotational fluctuation of a photoreceptor drum is suppressed at a high-precision by the use of a repetition control method, and an image forming apparatus which carries out image formation using this drive control method.
Further, it is the second object of the present invention to provide an image forming apparatus by which the problem to be produced in employing a rotational speed control method is eliminated.
Accordingly, to overcome the cited shortcomings, the abovementioned objects of the present invention can be attained by motor controlling methods and image-forming apparatus described as follow.
(1) A method of controlling a motor for driving a photoreceptor drum, comprising the steps of: detecting angular velocity signals by means of angular velocity detecting device disposed on an axis of the photoreceptor drum, which is driven by the motor to form a latent image on its circumferential surface; finding deviations from a reference angular velocity, based on the angular velocity signals detected by the angular velocity detecting device; storing a profile of the deviations within a one-revolution of the photoreceptor drum in a storage section, while revising the profile already stored in the storage section in real-time base; applying an arithmetic processing to an angular velocity signal, being one of the angular velocity signals, detected at a current rotational-position of the photoreceptor drum currently rotating, by referring data included in the profile obtained in a preceding one-revolution of the photoreceptor drum; and controlling the motor, based on results of the arithmetic processing for the angular velocity signals, so as to compress the deviations from the reference angular velocity as small as possible.
(2) The method of item 1, wherein the data correspond to a same position as the current rotational-position or a position near the current rotational-position.
(3) The method of item 1, wherein the detecting step of detecting the angular velocity signals is commenced, after a rotational velocity of the motor reached to a target value, and then, a waiting time interval for stabilizing mechanical fluctuations of the motor has elapsed.
(4) An apparatus for forming an image, comprising: a photoreceptor drum to form a latent image on its circumferential surface; a motor to drive the photoreceptor drum; an angular velocity detecting device to detect angular velocity signals, the angular velocity detecting device being disposed on an axis of the photoreceptor drum; a controlling section to control the motor and to find deviations from a reference angular velocity, based on the angular velocity signals detected by the angular velocity detecting device; a storage section to store a profile of the deviations within a one-revolution of the photoreceptor drum in it, while revising the profile already stored in the storage section in real-time base; and an arithmetic processing section to apply an arithmetic processing to an angular velocity signal, being one of the angular velocity signals, detected at a current rotational-position of the photoreceptor drum currently rotating, by referring data included in the profile obtained in a preceding one-revolution of the photoreceptor drum; wherein the controlling section controls the motor, based on results of the arithmetic processing for the angular velocity signals, so as to compress the deviations from the reference angular velocity as small as possible.
(5) The apparatus of item 4, wherein the data correspond to a same position as the current rotational-position or a position near the current rotational-position.
(6) The apparatus of item 4, wherein the angular velocity detecting device commences detecting the angular velocity signals, after a rotational velocity of the motor reached to a target value, and then, a waiting time interval for stabilizing mechanical fluctuations of the motor has elapsed.
(7) The apparatus of item 4, wherein a diameter of the photoreceptor drum is an integral multiple of a diameter of a peripheral roller rotating in contact with the photoreceptor drum.
(8) An apparatus for forming an image, comprising: a photoreceptor drum to form a toner image on its circumferential surface; a motor to drive the photoreceptor drum; a mark writing device to intermittently write each of marks on the photoreceptor drum at constant time intervals; a mark detecting device to detect each of the marks written by the mark writing device; a storage section to store mark-interval values between the marks detected by the mark detecting device; an arithmetic processing section to calculate rotational characteristics of the photoreceptor drum from the mark-interval values stored in the storage section; and a controlling section to control the motor, based on the rotational characteristics of the photoreceptor drum, calculated by the arithmetic processing section, so as to keep a circumferential surface velocity of the photoreceptor drum as uniform as possible.
(9) The apparatus of item 8, further comprising: a mark cleaning device to clean the marks, written by the mark writing device and developed with toner on the circumferential surface of the photoreceptor drum, before transferring the toner image onto a recording medium; and a toner recycling section to collect toner cleaned by the mark cleaning device and to convey the toner to a developing section so as to reuse the toner for developing.
(10) The apparatus of item 8, wherein a full color toner image is formed by overlapping a plurality of unicolor toner images on an intermediate transfer belt or a recording medium, and each of the plurality of unicolor toner images is formed by each of a plurality of unicolor image forming units included in the apparatus; and wherein the photoreceptor drum is employed for each of the plurality of unicolor image forming units.
(11) The apparatus of item 8, further comprising: an image exposing section to expose an image onto the photoreceptor drum, so as to form a latent image, which is developed with toner to form the toner image; wherein the image exposing section also serves as the mark writing device.
(12) The apparatus of item 8, wherein the marks are written on a non image-forming area of the photoreceptor drum.
(13) The apparatus of item 8, further comprising: a time interval changeover section to change a value of the constant time intervals, at which each of the marks is intermittently written, corresponding to a rotational frequency of the photoreceptor drum.
(14) A method of controlling a motor for driving a rotational body, comprising the steps of: intermittently writing each of marks on the rotational body at constant time intervals by means of a mark writing device; detecting each of the marks, written by the mark writing device, by means of a mark detecting device; storing mark-interval values between the marks detected by the mark detecting device in a storage section; calculating rotational characteristics of the rotational body from the mark-interval values stored in the storage section by means of an arithmetic processing section; and controlling the motor by means of a controlling section, based on the rotational characteristics of the rotational body, calculated by the arithmetic processing section, so as to keep a circumferential surface velocity of the rotational body as uniform as possible.
(15) The method of item 14, wherein the controlling section includes a motor-drive changing section to change a motor-drive command value, based on a calculation result of the arithmetic processing section.
(16) The method of item 15, wherein the controlling section controls the motor so as to compensate a delay time generated at a time when the motor-drive command value is calculated from the rotational characteristics of the rotational body, based on a reading delay time value, from a writing position at which a mark, being one of the marks, is written by the mark writing device, to a detecting position at which the mark is detected by the mark detecting device.
(17) The method of item 16, wherein the motor-drive changing section changes the motor-drive command value, based on the rotational characteristics of the rotational body calculated within a preceding one-revolution of the rotational body, so as to keep the circumferential surface velocity of the rotational body at a constant value.
(18) The method of item 17, wherein, during a velocity controlling operation for the rotational body, the mark writing device constantly writes each of the marks and the mark detecting device constantly detects each of the marks, and the mark-interval values stored in the storage section are revised in a real time base while the reading delay time value is compensated for, to continuously perform the velocity controlling operation for next revolution of the rotational body.
Further, to overcome the abovementioned problems, other motor controlling methods and image-forming apparatus, embodied in the present invention, will be described as follow:
(19) A drive control method of a photoreceptor drum characterized by comprising the steps of: storing a one-rotation profile of a photoreceptor drum, which is rotated by a drive motor to carry out image formation, as renewed in real time on the basis of an angular speed signal detected by an angular speed measuring means mounted on the drum shaft of the photoreceptor drum; carrying out an operation processing of angular speed information detected at the present drum position of the rotating photoreceptor drum through reading out for reference the stored profile at the drum position of one rotation before or data in the neighborhood of that; and outputting an order value to said drive motor on the basis of the result of the operation processing.
Further, it is a desirable mode of practice that the acquisition of the aforesaid profile is started after the passage of waiting time from timing when the aforesaid drive motor reaches to the target speed to timing when the mechanical fluctuation is subsided.
(20) An image forming apparatus characterized by comprising: a photoreceptor drum rotated by a drive motor for carrying out image formation; an angular speed measuring means mounted on the drum shaft of said photoreceptor drum; a storage for storing a one rotation profile of the photoreceptor drum obtained by an angular speed signal detected by said angular speed measuring means as renewing it in real time; an operation processing section for carrying out an operation processing of angular speed information detected by said angular speed measuring means at the present drum position of the rotating photoreceptor drum through referring to the stored profile at the drum position of one rotation before or data in the neighborhood of that; and a control section for outputting an order value to said drive motor on the basis of the result of the operation by said operation processing section.
Further, it is a desirable mode of practice that the diameter of the aforesaid photoreceptor drum is in a relationship of an integral multiple with the diameter of a peripheral member rotating in contact with said photoreceptor drum.
(21) A rotational speed control method characterized in that a mark writing means for writing marks at constant intervals on a rotary body rotated by a drive motor, a mark detecting means capable of reading the written marks at any time, a storage means for storing the values of the intervals of the marks read by said mark detecting means, an operation processing means for calculating the rotational characteristic of the rotary body from the interval values of the marks stored in said storage means, and a motor drive changing means for carrying out the change over of the drive order values of said drive motor from a digitized result of the operation processing, are included in order to perform a drive controlling operation to make constant the peripheral speed of the rotary body.
(22) An image forming apparatus characterized by comprising: a mark writing means for writing marks at constant time intervals on a photoreceptor drum rotated by a drive motor for carrying out image formation; a mark detecting means capable of reading the written marks at any time; a storage means for storing the values of the interval of the marks read by said mark detecting means; an operation processing means for calculating the rotational characteristic of the photoreceptor drum from the interval values of the marks stored in said storage means; a motor drive changing means for changing over the drive order values of said drive motor from the digitized result of the operation processing; a cleaning means dedicated to the marks only for removing the marks which have been written by said mark writing means and visualized by a developing means before image transfer; and a recycling means for conveying toner particles collected by said cleaning means dedicated to the marks only to said developing means.